One of things I find I like so much about green roofs is that they save money for the owners. When discussing "green" technology, many of them are not cost effective or economically efficient. On another blog I frequent, called Dollars and Sense, found at http://www.economicefficiency.blogspot.com, they discuss whether certain technologies make economic sense.
In my opinion, if a solution to a problem isn't cost effective, it just won't take off and gain widespread acceptance.
In an article found on AIArchitect (AIA.org) I found the most relevant quote:
"...Green roofs last two to five times longer than traditional roofs, require less maintenance, save energy by regulating temperature variations, reduce sound pollution, lower stormwater utility fees, receive energy tax credits, and increase property values."
Clearly, this type of roof is a money-maker for the owners and the tenants, as well as contributing to the common good. The article also points out how this green roof is not a roof garden, with up to 6 inches of soil, but rather a true green roof. True green roofs require very little soil, no additional water, and use local plants.
Did I mention this was from 2004? Green roofs are good for the environment, and good for your wallet!